The present invention is related to a process for preparing chlorotrifluoroethylene homopolymers having a low molecular weight.
Oily low molecular weight chlorotrifluoroethylene homopolymer is useful as a lubricant grease, lubricant oil, electrical insulator oil, hydraulic liquid, and liquid level indicator, etc.
Japanese patent publication No. 8231802 (1996) discloses a fluoropolymer composition having a low steam permeability, an excellent chemical resistance, a low permittivity, etc., and useful for a moistureproof coating material for electronic parts by compounding a fluoropolymer having cyclic structures in the main chain with a low-molecular chlorotrifluoroethylene polymer having a number average molecular weight (Mn) of about 1000.
U.S. Pat. No. 3,067,074 (1962) discloses a slow burning propellant composition containing a chlorotrifluoroethylene polymer having a number average molecular weight of about 4000-6000 as a binder.
U.S. Pat. No. 3,130,158 (1964) discloses a dry lubricant comprising MOS2 and a solid chlorotrifluoroethylene polymer having an average molecular weight less than 25000.
A low molecular weight chlorbtrifluoroethylene polymer can be prepared by thermo-cracking a high molecular weight chlorotrifluoroethylene polymer or by directly polymerizing chlorotrifluoroethylene monomers. U.S. Pat. Nos. 2,664,449 (1953), 2,854,490 (1958), 2,909,503 (1959), 2,992,988 (1961), and 3,045,000 (1962), and British patent No. 712184 (1954) disclose the thermo-cracking process. The thermo-cracking process requires a high molecular weight chlorotrifluoroethylene polymer as a feed, which has to be prepared in advance by polymerizing chlorotrifluoroethylene monomers. Moreover, corrosive/toxic gases such as HCl and HF are also generated during the thermo-cracking process.
U.S. Pat. Nos. 2,770,659 (1956), 2,837,580 (1958), 2,915,483 (1959) and 3,054,785 (1962), and German patent No. 1034362 (1958) disclose a process for preparing a low molecular weight chlorotrifluoroethylene polymer by polymerizing chlorotrifluoroethylene monomers in a solvent of SOCl2 or PCl3, or a mixed solvent of SOCl2 or PCl3 and a perchloro alkane such as CCl4 and C2Cl4. One defect of this prior art process is SOCl2 and PCl3 being corrosive, which renders the handling thereof difficult.
U.S. Pat. No. 2,706,715 (1955) discloses a process for preparing a low molecular weight chlorotrifluoroethylene polymer by polymerizing chlorotrifluoroethylene monomers in CO2 solvent, at 400xc2x0 C., 250 psi and in the presence of t-butyl hydroperoxide as an initiator. This process is carried out at a very high temperature, which is not desirable in the aspects of safety and operational cost, and corrosive/toxic gases such as HCl and HF are easy to be formed at such high temperature. In addition, the distribution of the molecular weight of the chlorotrifluoroethylene polymer prepared by this process is wide.
U.S. Pat. No. 2,766,299 (1956) discloses a process for polymerizing chlorotrifluoroethylene comprising subjecting to a temperature of about 350xc2x0 C. a gaseous mixture containing chlorotrifluoroethylene monomers and chlorine. This process also suffers the same defects of the above-mentioned high temperature process and the corrosive/toxic gases of HCl and HF.
U.S. Pat. No. 2,705,706 (1955) discloses a process for preparing a low molecular weight chlorotrifluoroethylene polymer by polymerizing chlorotrifluoroethylene monomers at 70-200xc2x0 C. and 15000-30000 psi. The high temperature and high pressure of this process are disadvantageous.
British patent Nos. 712152 (1954), 712184 (1954), and 796326 (1958), and German patent Nos. 934309 (1955) and 1052969 (1959) disclose a process for preparing a low molecular weight chlorotrifluoroethylene polymer by polymerizing chlorotrifluoroethylene monomers in a solvent of CCl4, CHCl3, C2Cl4, or Cl3CF, at 100-180xc2x0 C., 550 psi and in the presence of an initiator. In addition to the undesired high temperature and high pressure, the haloalkane solvents have been proved to be a factor causing cancer.
Japanese patent publication No. 52073802 (1977) discloses a process for preparing a low molecular weight chlorotrifluoroethylene polymer by oilgomerization of chlorotrifluoroethylene monomers in dimethylformamide (DMF) and in the presence of a catalyst of Me4N+Fxe2x88x92 for 24 hours, followed by dimerization of the oligomer, and chlorination in CCl4. This process is complicated, and CCl4 used is a carcinogen.
A primary objective of the present invention is to provide a process for preparing a chlorotrifluoroethylene homopolymer, wherein a chlorotrifluoroethylene homopolymer is synthesized under mild conditions through one single step.
The process of the present invention comprises polymerizing chlorotrifluoroethylene monomers in an ester solvent and in the presence of a peroxide such as t-butyl peroxypivalate as a radical initiator. The polymerization application can be carried at about 60xc2x0 C., and the resulting chlorotrifluoroethylene homopolymer has a number average molecular weight (Mn) of about 1700. The process of the present invention has advantages not only in using the chlorine-free ester solvent, which is less toxic and corrosive in comparison with the solvents used in the prior art, but also in a very high yield of greater than 90%.
The invention of the present application provides a process for preparing a chlorotrifluoroethylene homopolymer, which comprises polymerizing chlorotrifluoroethylene monomers in an ester solvent and in the presence of a peroxide as a radical initiator.
A suitable ester solvent for use in the process of the present invention has the following formula: RCOOxe2x80x94R1, wherein R is H or C1xcx9cC4 alkyl, and R1 is C1xcx9cC5 alkyl. Preferably, the ester solvent is ethyl acetate. A suitable amount of the ester solvent used in the polymerization reaction ranges from 0.1 to 100 ml per gram of the chlorotrifluoroethylene monomers, preferably 1 to 10 ml, and more preferably 2.1 to 2.3 ml.
A suitable peroxide for use as the radical initiator in the process of the present invention includes (but not limited to) bis-4-t-butylcyclohexyl peroxydicarbonate, t-butyl peroxypivalate and diisopropyl peroxydicarbonate, wherein t-butyl peroxypivalate is preferred. A suitable amount of the peroxide used in the polymerization reaction ranges from 0.1 to 20%, preferably 2.4 to 5.3%, based on the weight of the chlorotrifluoroethylene monomers.
The polymerization reaction of the process of the present invention can be carried out at a temperature ranging from xe2x88x9220 to 200xc2x0 C., preferably from 20 to 160xc2x0 C., and more preferably about 60xc2x0 C.